Oil well heating apparatus



Sept. 12, 1967 J, F SCOTT 3,341,688

OIL WELL HEATING APPARATUS Filed May 12, 1964 4 Sheets-Sheet l INVENTOR.

JOSEPH F SCOTT a 25mm, MM RJ Sept. 12, 1967 J. F. SCOTT 3,341,688

OIL WELL HEATING APPARATUS Filed May 12, 1964 4 Sheets-Sheet 2 INVENTOR.

JOSEPH F SCOTT Sept. 12, 1967 J. F. SCOTT OIL WELL HEATING APPARATUS 4 Sheets-Sheet- 5 Filed May 12, 196

FIG. 7

INVENTOR.

JOSEPH F SCOTT 6 a. W. 0 2 0 Q 8 B 2 w J 8 4 a w mmw m ,va 3 w 7 -rwn HHWI'ITZ|J[II 3 4 7 7 6 w 9 4 a a 9 1 w 9 6 V 8 i Q a p 12, 1967 .1. F. SCOTT OIL WELL HEATING APPARATUS 4 Sheets-Sheet 4 Filed May 12, 1964 [NVENTOR JOSEPH F SCOTT United States Patent 3,341,688 OIL WELL HEATING APPARATUS Joseph F. Scott, Chagrin Falls, Ohio, assignor to American Thermoelectric Corp., a corporation of Ohio Filed May 12, 1964, Ser. No. 366,747 11 Claims. (Cl. 219-277) This invention relates to well, or bore hole, heating apparatus and more particularly, to an improved electrical apparatus for heating the fluid in a well.

It is known in the art of extracting fluid from a well that productivity of a well increases with the temperature of the well fluid. Numerous attempts have been made to provide heating apparatus for heating the fluid in a well. For example, it is knOWn to employ a closed loop circulating hot water system for heating the fluid in a bore hole. In this system, a boiler is employed on the surface of the earth and heated water is pumped into the bore hole through conduits defining a closed circulating system. This system, however, exhibits numerous disadvantages. For example, much of the heat has dissipated before the water reaches the bottom of the bore hole, further, it is difficult to control closely the temperature of the bore hole, this temperature control being essential for proper heating of an oil well. If the fluid in an oil Well is heated too high, the heat causes chemical action which decomposes or deteriorates the oil. Further, it is difiicult to heat an oil well when the depth of the bore hole is great, for example, several thousand feet. Attempts have been made to employ electrical heating apparatus, however, numerous problems have been encountered with this type heating apparatus. For example, it is extremely difficult to obtain uniformity of heat dissipation and hot spots develop in the heaters which cause decomposition of the oil. Further, once a hot spot develops, it is self-generating and grows in size and ultimately decomposes the oil. It is known in the art to employ in an oil well a Calrod type heater in which power is dissipated at a very high rate per square inch; for example, these devices radiate heat of the order of 500 watts per square inch. These heaters, however, cause decomposition of the oil and are therefore unsatisfactory. Further, if attempts are made to decrease the rate of heat dissipation, insuflicient heat is generated to raise the temperature of the fluid in the well.

Accordingly, it is an object of this invention to provide a bore hole heater device which obviates the above disadvantages.

It is another object of this invention to provide a novel and improved electrical bore hole heating apparatus which can be closely controlled to regulate the temperature of the fluid in a bore hole.

It is a further object of this invention to provide an oil well heating apparatus with a temperature responsive resistance such that the well fluid temperature may be measured at a point remote from the heater.

Another object of this invention is to provide a bore hole heating apparatus which dissipates heat with a relatively low power density per square inch.

Yet another object of this invention is to provide a bore hole type heating apparatus which distributes heat uniformly over a relatively large surface area.

Another object of this invention is to provide an oil well heating apparatus with means for centralizing the oil well heater relative to the casing.

Still another object of this invention is to provide an oil well heating apparatus with an improved electrical connector such that fluids are prevented from making contact with the electrical wires supplying energy to the heating element, or to the heating element.

A still further object of this invention is to provide an electrical oil well heating apparatus with a clamp which acts as a spacer unit to maintain spacial relationship between the heating apparatus and the well casing.

Still another object of this invention is to provide an oil well heating device with an electrical unit having a low power density and a covering which protects the heating element from the fluids in the bore hole to thereby prevent chemical action taking place in the bore hole fluid.

These and various other objects and features of the invention will be more clearly understood from a reading of the detailed description of the invention in conjunction with the drawing in which:

FIGURE 1 is a view, in elevation, of the control box and switch employed in the electrical system of this invention;

FIGURE 2 is a view, in elevation, partly in section, of a well head employing this invention;

FIGURE 3 is a view, in elevation, partly in section, of the bore hole including the oil zone and having in the bore hole a heater according to one illustrative embodiment of this invention;

FIGURE 4 is a view in elevation, partly in section, to an enlarged scale of an electrical receptacle-plug assembly employed in this invention;

FIGURE 5 is a view in section of the receptacle-plug assembly of FIGURE 4 taken along the lines 55 of FIGURE 4;

FIGURE 6 is a view in section of a portion of the receptacle of FIGURE 5 with the connector cables removed;

FIGURE 7 is a view in elevation and in section of the plug assembly of FIGURE 5;

FIGURE 8 is a view in elevation of the assembly of FIGURE 7 taken along the lines 8-8 and looking in the direction of the arrows;

FIGURE 9 is a view in elevation of the assembly of FIGURE 7 taken along the lines 99 and looking in the direction of the arrows;

FIGURE 10 is a view in section, to an enlarged scale, taken along the lines 1010 of FIGURE .3; and

FIGURE 11 is a view in elevation, partly broken away, of the centralizer of FIGURE 10.

FIGURE 1 shows a pole, such as utility pole, 10 on which is mounted a suitable electrical control box 14 and a switch 16 connected to a source of power through a cable lead-in 17 and three power lines 18 which may advantageously be from a three-phase generator. The switch 16 may be of a well known type of three-phase switch of the three-pole, double-throw type and the switch 16 is connected to the control box 14 by means of a suitable cable 19. The electrical wiring from the control box 14 to the bore hole fluid heating apparatus is in a cable 20, which cable includes leads to a thermostat and to a plurality of heating units which will be subsequently described. The electrical control system in the control box 14 controls the power delivered to the Well heater and is the subject matter of US. patent application Ser. No. 366,818, filed concurrently herewith.

FIGURE 2 is a view in elevation, partly in section, of a portion of a well head. The well head is defined by the end of a casing 22 and a fluid tight cap, or endwall 23 secured thereto such as by welding. The cable 20 projects through a gas tight fitting 24 in the endw-all 23 and is held or secured to a section of the well tubing 25 by means of a suitable clamp 26. A sucker rod 28 of the type well known in the art projects through a stuffing box 30 in fluid sealing relationship. A fluid exhaust pipe 32, projects from the tubing 25 and extends to a suitable tank or storage reservoir not shown. A joint 34 is located adjacent the endwall 23 to provide a support for the tubing 25.

FIGURE 3 shows the oil zone portion of the bore hole in which the casing 22 terminates in a reduced diameter casing section 36 secured to casing 22 and having passages 42 thercthrough for the admission of oil and other liquids into the bore hole. The cable is securely held in engagement with the tubing 25 and is supported where it passes over each coupling 34 by means of a clamp having a pair of straps 41 thereon, the details of which will be subsequently described. The casing section 36 constitutes a perforated liner; for example, a six-inch inside diameter pipe having longitudinal perforations 42 to permit fluid to enter the interior of the casing section 36.

The heating apparatus includes a perforated nipple 44 which permits the entry of the oil bearing liquid into a pump 43. This pump 43 is a conventional type pump of the type frequently employed in oil wells or other liquid wells. Beneath the perforated nipple 44 and connected thereto by means of a double-threaded sleeve or coupling 34 is a short section of tubing 46 which is connected by means of an adapter connector 48 to a heater unit 50. The heater unit 50 includes an elctrical fluid sealed plug and receptacle termination 52 for the cable 20 and includes at least three spaced heater elements 54 which are radially spaced about the heating section 50 and extend longitudinally thereof and are connected to the cable in a manner which will be subsequently described in detail. The heater elements 54 are connected together at their lower extremities by means of a conducting bus 55. Advantageously, the heating section 50 is located beneath the pump and preferably on the lowermost section of the apparatus to obtain maximum utilization of the heat from the heater section 50 because the heated fluids tend to rise. Further, by locating the heating section adjacent the bottom of the well, fluids normally having a relatively high density are caused to rise and to be pumped up through the pump section 43. Advantageously, a temperature responsive variable resistance sensor 56 is located on pipe 53 above the heater elements 54, as viewed in FIGURE 3, so that the sensor element accurately measures or responds to the temperature of the fluid in the bore hole and is not directly affected by the temperature of the heater elements.

Advantageously, the lower end of the heating elements 54 is spaced from the lower end of pipe 53 to permit a bumper-like centralizer 58 to be mounted on pipe 53 to protect the heating section 50 from the well casing 22 and the perforated liner 36. Also advantageously, pipe 53 is open at the lower end thereof to permit entry of the bore hole fluid so that both surfaces of pipe 53 act as heat radiators. Centralizer 58 includes a plurality, such as two, diametrically opposed, radially extending members 59 mounted on the pipe 53 by means of an upper and a lower strap 60, 61, respectively. A second centralizer 62, Which may be structurally identical with centralizer 58, is mounted on pipe section 46 and radially positioned at 90 relative to centralizer 58 to protect the upper end of heater section 50.

FIGURE 4 is a plan view, partly in section, and to an enlarged scale of the plug and receptacle assembly 52 shown in FIGURE 3. The plug and receptacle assembly 52 includes a plug assembly 63 having a shell 64 which is preferably substantially rectangular and may be formed of any suitable metal which does not react with the chemicals in the bore hole, for example, stainless steel. The shell 64 has a cover 65 which is secured in place by means of a group of four flathead screws 66, only one of which is shown, which pass through the cover 65 and engage the shell 64. A threaded receptacle assembly engaging stud 67 is rotatably mounted in plug assembly 63 for securing the plug assembly 63 to a receptacle assembly 68. The cable 20 includes five conductors, three of which supply three phase power from the respective phases of the supply line and two of which are connected to a serially connected thermostat 69 and the sensor 56. In FIGURE 4 only two of phase connecting leads 70, 71 are shown, the third being located above the stud 67. Conductors 72, 73 are connected to the thermostat and sensor in a manner which will be subsequently described. In the plug assembly 63, leads 70, 71 are connected to a pair of socket contacts 74, 75, respectively. The contacts, such as 74, 75 are imbedded in suitable annular members 77 which are spaced about the shell 64 and are formed of phenolic resin, or other insulating medium. A third contact 76 is shown in FIGURE 7. The engaging stud 67 is mounted in a freely rotatable relationship in a cylindrical shell 80 by means of a snap ring, or retaining ring, 82 and a washer 83 which engages a reduced portion of the stud 67 and also engages the end of the cylindrical passage shell defining member 80, An O-ring $4 is provided in an annular recess 85 in the engaging stud 67 to define a fluid seal between the stud and the cylindrical passage 80. The outer end or head 86 of the stud 67 preferably has a hex-shaped aperture 87 to re ceive a Wrench for rotating the stud. The opposite end of the stud 67 is threaded at 88 to threadably engage a portion of the receptacle assembly 68. The plug assembly 63 includes an O-ring 89 in an annular notch 91 to form a fluid seal between plug assembly 63 and receptacle or connector assembly 68.

FIGURE 5 is a view of the receptacle assembly 68 taken along the lines 5-5 of FIGURE 4, and FIGURE 6 is a sectional view of a cylindrical pin mounting portion 92 taken along the lines 6--6 of FIGURE 5. Portion 92 is cylindrical and has a plurality of pins 93, 94, 95, 96 and 97 each encircled by insulation and spaced about an internally threaded, axially aligned, aperture 98. The cylindrical portion 92 is preferably stainless steel to prevent chemical reaction with the bore hole fluid passing through pipe 50. The receptacle assembly 68 includes a flange portion 103 which is formed integrally with cylindrical portion 92 and which is curved to fit the pipe section 53. The curved portion has a plurality of apertures 104 therein through each of which a screw 105 extends to threadably engage the pipe section 53 which supports or defines the base of the heater section 50. These screws 105, only two of which are shown in dotted outline in FIGURE 4, are preferably flat-headed and are threadably inserted into the pipe 53 until the head is flush with the outer curved surface of flanges 103. The plug and receptacle assembly 63 includes a substantially cylindrical phenolic, or other insulating plastic member, 106 which supports a plurality of socket contacts 108, 109, 110, 111 and 112 which contacts engage the respective pins 93, 94, 95, 96 and 97 of the receptacle assembly to establish an electrical connection to the electrical portions of the heater section. As shown in FIGURE 4, suitable conductors are provided for connecting the contact pins to the sections of the heater. In this particular example, a conductor 113 is connected to contact pin 93 which pin is shown in FIGURE 6 without conductor 113. A conductor 114 is connected to contact pin 97 and conductor 115 is connected to contact pin 94 to supply three-phase power to one of the heater elements 54.

The sensor 56 is serially connected to the thermostat 69 by suitable wires, not shown, and is connected to pin 96 by means of conductor 117. The thermostat 69 is mounted on the exterior surface of pipe 53 beneath one of the heater elements 54 and is connected to the pin 95 of the receptacle assembly by means of conductor 116, which conductor is incapsulated with conductor 117 in resilient material 118 in the region adjacent the pipe 53 such that materials in the bore hole fluid entering thelower end of the pipe 53 cannot force the cables against the edges of an aperture or hole 120 in pipe 53 through which the conductors 116, 117 pass. The thermostat 69 is mounted substantially flat on the outer surface of the pipe 53 and is insulated from the pipe by a layer of insulation such as glass cloth impregnated with epoxy resin. After the thermostat is positioned it is also covered with a layer of glass cloth and epoxy resin and the heater elements 54 are superimposed on this insulating layer, with one of the elements 54 covering the thermostat 69. The

thermostat is a temperature actuated switch which disconnects the power from the heating element through a control system such as the type disclosed in previously mentioned, concurrently filed, application Ser. No. 366,818. Preferably, but not necessarily, the thermostat is so de signed and connected in the heater control circuit to open the heater supply at a heater temperature of 260 F. plus or minus 5 F. It has been found that if the heater element is allowed to exceed this figure, chemical action of the oil takes place, decreasing the resulting usable prodnot.

The electrical corrections to each of the heater elements 54 are identical and therefore only one will be described in detail. As best seen in FIGURE 5, which is a section taken along the lines 5-5 of FIGURE 4, the conductor 113 passes through a copper Washer 122 where it is soldered as indicated at 123. The copper washer 122 is also soldered at 124 to a copper bus bar 126. The copper bus bar 126 is a fiat strip of copper which overlaps and electrically connects with one of the heater elements 54. In this particular instance, the resistive material defining the heater elements 54 is sprayed upon a layer of glass cloth 127 impregnated with epoxy resin. All three of the heater elements 54 may be simultaneously formed by placing masking tape strips at spaced, preferably radial, intervals and spraying a resistive material such as metal or carbon upon a layer of epoxy resin impregnated glass fibre cloth and then removing the masking tape to separate sections of the resistive material into three identical heater elements 54. The conductors, such as 113, 114, are incapsulated in a mass of resilient dielectric material 128 to prevent the leads from being bent =by material in the bore hole fluid at the point where they enter the apertures, such as aperture 129 in the pipe 53, for conductor 114. As best seen in FIGURE 3, the heater elements 54 are spaced radially around the pipe 53 and connections similar to that just described may be made at points radially spaced 30 apart on the surface of the pipe. The opposite, or lower terminal, of the heater element is defined by the bus bar 55, shown in FIGURE 3, which connects the three heater elements in a Y connection. Advantageously, the heaters provide a relatively large heater area for the power to be dissipated; for example, in one specific illustrative single-phase embodiment, the combined heater element width is 2.8 inches, the length is 560 inches, the resistance is 3.25 ohms and the power dissipation of the heater is 12,700 watts with 203 volts impressed across the heater element. Thus, in this specific embodiment, the power density in watts per square inch is 8.2. In an illustrative three-phase embodiment, each element has a width of 1.24 inches, an element length of 420 inches per phase, a resistance of 27.70 ohms and with a voltage of 427 volts measured phase-to-phase, a power density of 8.6 watts per square inch. The heater elements are insulated from the pipe by the layer of epoxy resin impregnated glass fiber cloth 127 as previously mentioned, and the heater elements are also covered with a corresponding second layer 130 of glass cloth impregnated with epoxy resin. Preferably, these layers are of the order of .025 inch in thickness to provide adequate insulation between the heater elements 54 and the pipe section 53 and to prevent contact with the bore hole fluid. Because of the relatively low power density and the accurate control of the temperature of the heater elements by means of the sensor 56 and thermostat 69, adverse chemical action does not take place in the bore hole fluid.

In one convenient method for forming the insulating coating on the pipe 53, the glass cloth is first out to a length which is about longer than the circumference of pipe 53 to allow for shrinkage and coated with epoxy resin, as by spraying. The coated cloth is then wrapped around the pipe 53 and covered with a vacuum bag. The covered pipe is then placed in a heat treating chamber and heated to a temperature to cause the resin to penetrate the cloth and adhere to pipe 53. While the heat treating step is being accomplished, a suitable hose, connected to the interior of the vacuum bag, is employed to remove air from the interior of the bag so that the impregnated cloth is forced against the pipe 53 by the fluid pressure on the exterior of the bag. After the heat treating step, longitudinal masking tapes are placed on the coated cloth to cover areas which are to be free of resistive material. The resistive material is now sprayed, or otherwise formed, on the impregnated cloth to the desired thickness and the masking tape removed to form insulating areas between heating elements 54.

FIGURE 7 is a view in elevation and in section of the plug assembly 63 which is employed to connect the cable 20 to the receptacle assembly 68. FIGURE 8 is a view of the plug assembly of FIGURE 7 taken along the lines 88 and looking in the direction of the arrows. FIGURE 9 is a view of the plug assembly of FIGURE 7 taken along the lines 9-9 and looking in the direction of the arrows. The plug assembly includes a bumper 13-1 preferably formed of plastic material and secured in a substantially rectangular recess 132'in the lower end of the shell 64. The bumper 131 has a tapered lower surface 133 so that materials in the bore hole fluid will be deflected away from the plug assembly 63. The bumper 131 also has a concave surface 134 for snugly engaging pipe 53 when the plug assembly 63 engages the receptacle assembly 68.

FIGURE 10 is a view in section of the first centralizer 58, taken along the lines 10-10 of FIGURE 3, to an enlarged scale and FIGURE 11 is a fragmentary view in elevation of the centralizer of FIGURE 10. In FIGURE 10, the pair of radially extending U shaped member 59 are secured on pipe section 53 by the strap assembly 60 which is identical to the strap 61 at the lower end of the centralizer 58. Each U shaped member 59 is generally U- shaped in cross section and has a pair of end portions 140, each having a pair of edges 142, 143 which engage the surface of the pipe 53 and a spaced apart portion 145 which is substantially parallel the pipe. These end portions 140 are connected by a pair of angularly disposed portions 146. Preferably, the strap assemblies 60, 61 are secured to the end portions 140 by means of rivets such as 148. The strap assembly 60 is preferably formed of a first portion and a second portion 152 joined together by forming or punching a tongue 153 out of a central portion of the second strap portion 152 and punching a hole 154 in the strap and inserting the tongue 153 through the hole 154 in the strap 150. The opposite ends of the straps are connected to a hook and a link arrangement so that the strap may be quickly tightened around the cable guard and pipe. The strap 150 terminates in a hook-shaped portion 155 which is welded or otherwise secured to strap 150 and engages one end of a link 156. The link 156 has a pair of opposed hook-shaped ends 157, 158 which hook into a pair of suitable apertures 159, 160 in a handle 161, as best seen in FIGURE 11. Strap 152 terminates in an end 163 which wraps around a bar 164 of the handle 161 to define a pivotal connection between the strap 152 and the handle 161. In mounting the centralizer on the pipe 53, the radially extending members 59 are manually held in position preferably diametrically opposed on the pipe 53 and the handle and link 161, 156 are released so that the straps 150, 152 may be reached around the pipe 53 and both guards 59. The tongue 153 of the strap 152 is engaged with the aperture 154 in a strap 150 and the link 156 is engaged with the hook 155. The handle 161 is now rotated into the position engaging pipe 53 as shown in FIGURE 10. The similar strap 61 is attached to the lower end of the guards 59 securely to hold the radially extending members 59 in position. Centralizers 58, 62 prevent the heater section 50 from contacting the inner surfaces of the bore hole liner 36 or the bore hole casings 22 and insure a substantially constant volume of bore hole fluid between the pipe section 53- and the liner 36 to thus obtain uniformity of heating of the fluid. The centralizer 62 on pipe section 46 is identical to centralizer 58. Preferably,

I? centralizer 62 is rotated 90 relative to centralizer '58 to protect the apparatus from moving into contact with casing 22 and liner 36, in a plane perpendicular to the plane containing centralizer 58 in FIGURE 3.

From the foregoing explanation, it is apparent that this novel heating apparatus, with its low power density heating elements 54, large heat radiating surfaces on both inside and outside of pipe section 53, centralizers which prevent damage to the heating section and assure uniformity of heating of the bore hole fluid, power controlling sensor and thermostat 69 achieve results which cannot be accomplished by the prior art devices. Further, these results are obtained by an apparatus which is so durable in construction that it can be economically and safely operated continuously for extended periods of time.

While I have shown and described one illustrative embodiment of this invention, it is understood that the concepts thereof may be applied to other embodiments without departing from the spirit and scope of this invention.

What is claimed is:

1. In a bore hole fluid heating apparatus, the combination comprising:

a cylindrical pipe;

resistive means on said pipe;

electrical means connected to said resistive means for supplying electrical energy thereto;

thermostat means adjacent said resistive means for accurately limiting the amount of power supplied to said resistive means; and

sensor means mounted on said pipe remote from said resistive means for sensing the temperature of the bore hole fluid and for closely controlling the power supplied to said resistive means.

2. The combination according to claim 1 further including centralizer means mounted on said pipe for maintaining the resistive means in spaced relationship relative to the bore hole liner.

3. The combination according to claim 1 further including centralizer means on said pipe above and below said resistive means for maintaining said pipe in spaced relationship relative to the bore hole.

4. In a bore hole fluid heating appartus, the combination comprising:

an elongated cylindrical pump section open at one end;

a perforated nipple section connected to the open end of said pump section;

a heater section open at both ends and connected to said nipple section and including a base member, an insulating layer on said base member, resistive means on said insulating layer, and an insulating layer on said resistive means; and

means for supplying electrical power to said resistive means including thermostat means operatively associated with said resistive means for controlling the power supplied to said resistive means; and temperature responsive sensor means mounted on said apparatus for sensing the fluid temperature in the bore hole.

5. The combination according to claim 4 further comprising a plurality of connectors, each connecting two of said sections, said means for supplying electrical power including a cable, the combination further including cable guard means connected to said cable and to said apparatus for retaining said cable in contact with each of said connectors.

'6. The combination according to claim 4 further comprising centralizer means mounted on each end of said heater section for maintaining said apparatus centrally of said bore hole.

7. In a well fluid heating apparatus, the combination comprising:

a tubular pump section;

a perforated nipple section coupled to said tubular pump section;

a cylindrical heating section coupled to said perforated nipple section, said heating section including a pipe having thereon a coating of non-conductive material, a coating of resistive material and a coating of nonconductive material, in that order;

electrical means for supplying electrical energy to said resistive coating;

sensor means operatively associated with said resistive coating for accurately controlling the temperature of said coating; and

thermostat means positioned intermediate said resistive coating and said pipe of said heating section for limiting the temperature of the resistive coating.

8. A bore hole fluid heating apparatus comprising:

a pump section open at one end;

a perforated nipple section connected to the open end of said pump section;

a heater section open at both ends and connected to said nipple section and including an insulating layer, resistive means on said insulating layer, a second insulating layer on said resistive means;

means for supplying electrical power to said resistive means including sensor means for accurately controlling the power supplied to said resistive means in accordance with the temperature of said bore hole fluid; and

connector means connecting said sections, said electrical supply means including a cable, said combination further including a plurality of cable guards for connecting said cable to said apparatus to bridge said cable over each of said connectors and wherein said insulating layers are impregnated glass cloth and wherein said resistance means includes a resistive metal coated on said glass cloth.

9. A bore hole fluid heating apparatus comprising:

a pump section open at one end;

a perforated nipple section connected to the open end of the pump section;

a heater section open at both ends and connected to said nipple section and including an insulating layer, resistive means on said insulating layer, a second insulating layer on said resistive means;

means for supplying electrical power to said resistive means including sensor means for accurately controlling the power supplied to said resistive means in accordance with the temperature of said bore hole fluid;

means for supplying electrical power to said resistive means including a cable, a plug mounted on said cable and a receptacle including a plurality of connectors mounted on said heater section and connected to said resistive means, which plug includes a housing with an aperture therein to receive said cable means for securing said plug to said receptacle, said plug joining said receptacle at right angles to the axis of said heater section and said plug further including a plurality of contact means spaced about said securing means.

10. The combination according to claim 9, further including bumper means mounted on the end of said plug.

11. A bore hole fluid heating apparatus comprising:

a pump section open at one end;

a perforated nipple section connected to the open end of said pump section;

a heater section open at both ends and connected to said nipple section and including an insulating layer, resistive means on said insulating layer, a second insulating layer on said resistive means;

means for supplying electrical power to said resistive means including sensor means for accurately controlling the power supplied to said resistive means in accordance with the temperature of said bore hole fluid; and

said electrical supply means includes a thermostat mounted on said heater section beneath said firstmentioned layer and beneath said resistive means,

said thermostat being serially connected to said sensor means.

References Cited UNITED STATES PATENTS Pennington 219277 10 Germain 2719-278 X Ackley 219-2177 X Cowdrey et a1. 219-635 X Spitz 219-2-77 X Williams et a1. 219278 X Bowman et a1. 219-277 RICHARD M. WOOD, Primary Examiner.

C. L. ALBRITTON, Assistant Examiner. 

1. IN A BORE HOLE FLUID HEATING APPARATUS, THE COMBINATION COMPRISING: A CYLINDRICAL PIPE; RESISTIVE MEANS ON SAID PIPE; ELECTRICAL MEANS CONNECTED TO SAID RESISTIVE MEANS FOR SUPPLYING ELECTRICAL ENERGY THERETO; THERMOSTAT MEANS ADJACENT SAID RESISTIVE MEANS FOR ACCURATELY LIMITING THE AMOUNT OF POWER SUPPLIED TO SAID RESISTIVE MEANS; AND SENSOR MEANS MOUNTED ON SAID PIPE REMOTE FROM SAID RESISTIVE MEANS FOR SENSING THE TEMPERATURE OF THE BORE HOLE FLUID AND FOR CLOSELY CONTROLLING THE POWER SUPPLIED TO SAID RESISTIVE MEANS. 